A tough little component for cars,flying vehicles and other mobility products in daily life

As increasing numbers of vehicles are replaced to the smarter ones with the internet connection and various sensors, they can drive autonomously, and will be more convenient and comfortable. However, this smartification also means that they use more and more electricity.

Based on theGreen Growth Strategy Through Achieving Carbon Neutrality in 2050, the Japanese government aims to ensure that all of new cars are electric ones at least by the mid-2030s, and it is likely that amount of electricity consumption will be rising by advances and dissemination of the mobility. But electricity is a limited resource. The resources to generate it are also limited, thus its amount we can use is limited. As mobility products become smarter, we must find ways to use electricity more efficiently, or else our planet will suffer the consequences.

That’s why we must carefully consider energy management as we electrify various vehicle types, and factors such as battery and motor performance present major challenges. One component can help overcome such obstacles to successful electrification: power semiconductors.

Semiconductors are used throughout our daily life. A wide variety of electric appliances rely on them to operate, such as air conditioners, rice cookers, washing machines, refrigerators, televisions, computers, smartphones, digital cameras and others.

Semiconductors are also used for mobility products in various situations. And are mounted in vehicles the sensors to process the images inside and outside of them, to measure the distance and to check the system conditions, and the processors to make decisions in autonomous driving, for their basic functions such as ”driving”, “turning” and “stopping”. Especially the power semiconductors are core parts of EVs among in-vehicle semiconductors, and they control extremely high power and voltage to drive the vehicles.

In line with the auto industry’s CASE (connected, autonomous, shared and electric) approach, in-vehicle semiconductors have become more important with the advancement in connected and automated vehicles. With so many built-in cutting-edge technologies, vehicles will essentially become mobile high-end computers. In other words, we are entering an era in which semiconductors will be key for improving mobility.

Just as the computer performance depends on the CPUs, vehicle performance depends on the in-vehicle semiconductors. However, simply focusing on performance alone when designing in-vehicle semiconductors does not produce optimal results. That’s because components used in vehicles need to not only perform well, but also withstand high voltages and currents as well as extremes of temperature, ranging from lows of around −40°C to highs of 125°C (roughly −40°F to 260°F). Moreover, they must be able to withstand high humidity along with strong vibrations and impacts, while continuing to function uninterrupted. In short, in-vehicle semiconductors need to be extremely tough. And when used in commercial trucks and new vehicle types such as eVTOL (electric vertical take-off and landing) “flying cars,”these components must be designed to withstand various types of loads not encountered in passenger automobiles.

As with other automotive components, a semiconductor malfunction could threaten passengers’ lives, which is why in-vehicle semiconductors must comply with the strict reliability requirements established for automotive applications while also achieving low environmental impact.

In order to realize the EVs, the mobile high-end computers, it is necessary to develop tough in-vehicle power semiconductors for use in energy management operations, and to ensure they can withstand in-vehicle usage conditions by using new materials named silicon carbide (SiC).

Compared with conventional types of semiconductors, SiC semiconductors offer higher performance. However, generic ones on the general market could not meet the required quality for mobility, and we could not guarantee the sufficient reliability for in-vehicle applications. For power semiconductors, material quality is a major determinant of their performance, and thus we needed to develop the materials themselves on our own.

To achieve the high quality and durability needed for the SiC semiconductors used on each automotive power semiconductor, they have been working to develop high-quality materials. DENSO has been developing the high quality materials to overcome the weak point of SiC, and finally made them tough enough to be mounted in vehicles. Inverters with DENSO’s SiC power semiconductors can be reduced by about 60% in volume, and by about 70% in electricity consumption compared with the conventional ones, and it leads to the miniaturization of the products and the improvement of the fuel consumption. It also reduces the amount of material required to commercialize products, lowers the products cost to realistic one for end users, and gives the interior of vehicles plenty of room to provide greater user comfort.

Why could DENSO develop the SiC semiconductors that can withstand stringent in-vehicle usage conditions and requirements?

Shoji Kanda from the Sensing Systems & Semiconductor Business Unit explains,

“DENSO has long been involved in developing semiconductors exclusively for vehicle use, which greatly helped us invent the new types of semiconductors.”

“DENSO has been involved with in-vehicle semiconductors since the early 1960s. At first, we used semiconductors supplied by other companies, but when these failed to meet operating requirements related to temperature ranges and so forth, we focused on developing our own, tougher semiconductors that could endure in-vehicle usage.”

“There were no automobile-specific semiconductors available anywhere in the world at that time, so we decided to develop them ourselves. So we founded a research facility with the goal of producing these components in-house.”

“CMOS IC” was one technology that resulted from various invention on the way to pursue tough in-vehicle semiconductors. IC is a small electronic element that switches over electric signals at high speed.

Kanda continues,

“When DENSO started to research in-vehicle semiconductors, older ICs predating these CMOS ICs one generation ago were being used in handheld calculators, microcomputers and the like. DENSO believed that in-vehicle semiconductors would be the key components for vehicles’ performance in near future, and was also convinced that ICs would be required less electricity consumption than ever when they have more functions. That’s why we focused on the CMOS IC, which first appeared in 1968.”

“Thanks to a new switching mechanism, this technology had the potential to achieve low-power operation. We sent our staff to Radio Corporation of America (RCA), which was a world leader in the industry at that time, to learn about state-of-the-art technologies. After our staff returned to Japan, they came together to form an elite team of engineers within DENSO.”

“We succeeded in developing our own CMOS IC in 1972, and in 1977 completed the world’s first automotive-use clock equipped with a CMOS chip.”

DENSO has been researching a new type of semiconductor that does not exist yet anywhere in the world. Determined to meet strict operating requirements, and leveraging skills and technologies gained in mobility-field development, we were able to create a tough SiC power semiconductor. Using its research results and experience, DENSO began full-scale development of its own power semiconductor in 2003, dividing up operations among multiple departments.

Kazuhiro Tsuruta of MIRISE Technologies, which is in charge of SiC-related development, remembers just how difficult the SiC power semiconductor project was:

“The spread of hybrid electric vehicles (HEVs) which began in the first decade of the 2000s resulted in strong demand for smaller power control units (PCUs), which were necessary to appropriately control the electric power for HEVs and EVs. Miniaturizing a component like this requires high efficiency heat radiation technology.”

“Back then, heat was typically dissipated from the back side of semiconductor chips in the PCU. However, because heat is generated from the interior of the chips, we came up with the idea that we could achieve a smaller PCU with higher radiation efficiency by radiating accumulated heat from the front surface as well as the back, so that was our development approach.”

“Because DENSO had already developed sophisticated cooling technologies for radiators, we used these to develop dual-sided cooling. Ultimately, we succeeded in creating a smaller PCU with excellent heat radiation. When we started its development, people criticized us, saying that our dual-sided cooling idea showed we were inexperienced amateurs. It’s true that we were challenging something so difficult that even veterans in the field wouldn’t have attempted it, and yes, the development process was really hard. On a technical level, it was extremely difficult to attach a heat-radiation plate to the front side of the chips.”

Even when the development team reached the stage where this feat had become technically possible, the challenges of mass production and so forth remained to put it to practical use. According to Tsuruta, one of the factors how DENSO can successfully put its products to the practical use is its vertical integrated development capabilities that covers the process from the development of the materials through manufacturing of the products and the system design.

Tsuruta explains,

“Even we have developed SiC power semiconductors, they are still more expensive than conventional ones by themselves. But if we could adopt an integrated development approach, from the production of the tiny chip through mobility system integration, and then make it part of the product of the inverter unit, we would be able to realize acceptable cost levels.”

“Even if it is difficult to put the semiconductors into practical use by themselves, we can commercialize them by our vertical integrated development. It is DENSO’s strength."

After development, the product was subjected to various endurance tests to ensure that it would operate normally under any conditions. We make products work actually in the extreme environment at a hundred and some dozens degrees Celsius or at minus dozens degrees Celsius in testing machines. And we find out any defects there and fix them repeatedly, and finally complete our tough semiconductors.

After about 25 years of sustained effort, DENSO completed its SiC power semiconductor that could be used in actual automotive applications. On December 9, 2020,Toyota launched new Mirai, which adopted these semiconductors.

DENSO took the following approaches to create a stronger SiC semiconductor:

1. In-house production of a device that is not only smart, but also meets the stringent requirements of in-vehicle usage

2. Application of technologies that have been developed for mobility products

3. Leveraging overall company strengths through vertically integrated development to achieve miniaturization and high efficiency of the products

DENSO has succeeded in developing the tough SiC making use of these strength. Ever since the original semiconductor development team was formed in the 1960s, the Semiconductor Business Unit has spent many years manufacturing semiconductors for the world, while the research center has spent nearly 30 years working tirelessly with delicate SiC material toward the ultimate goal of commercialization. Their strong determination lead this task to success.

DENSO’s SiC is just getting started for the electrification of vehicles. As the transition to EVs continues to accelerate, the performance of these products will reflect on the value of DENSO semiconductors as a whole. With the goal of promoting further innovations and improvements throughout society through our revolutionary technologies,DENSO is continuing to develop comprehensive technologies.

SiC power semiconductors have wide-ranging potential. For example, if they are used in future fordynamic wireless power transfer systems, they could bring huge improvements in miniaturization and efficiency for the power supply systems. According to Tsuruta and Kanda, DENSO has already succeeded in realizing practical applications for SiC material, thus DENSO must make use of the experience gained through that process to meet new user and industry needs moving forward. In this way, DENSO can respond to future demand for new-material development by calling on its experience and technologies gained through SiC-component development.

Power semiconductors for the mobility field can be used in other fields as well. Today semiconductors are often utilized in the digital home appliances that are used indoors, and as smart city projects spread throughout society, more outdoor devices will be becoming smarter and more digitalized, fueling demand for tough and durable semiconductors.

For example, infrastructure systems are on condition that they operate 24 hours a day. They are exposed to wind, rain, strong sunlight and other such weather conditions. Tough semiconductors are essential to ensure such systems operate reliably. Moreover, electrification is expanding to other mobility areas such as eVTOL flying cars, construction equipment and commercial trucks, all of which have stricter durability and resistance requirements for their semiconductor components. DENSO’s power semiconductors make stable operation possible in these and other fields.

In the near future, electricity will be used in a much wider range of settings and applications. Therefore, DENSO will continue disseminating its proprietary power semiconductors developed in-house to contribute to realize the carbon-free society.